The crews from the Vietnamese and Chinese coast guards shook hands and took photos as they met last month, sharing platters of fruit and raising their glasses for a toast. Now, they are in a tense standoff in the South China Sea.

Southeast Asian foreign ministers said they were concerned about a rise in territorial tensions in the South China Sea, calling on all parties including China to show “self-restraint” after Chinese and Vietnamese ships collided near disputed islands.

Vietnam’s leaders face growing pressure to challenge China in international court, risking economic retaliation by its largest trading partner, after a Vietnamese fishing boat collided with a Chinese ship and sank.